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Network Working Group                                          J. HodgesRequest for Comments: 2830                                    Oblix Inc.Category: Standards Track                                      R. Morgan                                                      Univ of Washington                                                                 M. Wahl                                                  Sun Microsystems, Inc.                                                                May 2000Lightweight Directory Access Protocol (v3):Extension for Transport Layer SecurityStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2000).  All Rights Reserved.Abstract   This document defines the "Start Transport Layer Security (TLS)   Operation" for LDAP [LDAPv3,TLS]. This operation provides for TLS   establishment in an LDAP association and is defined in terms of an   LDAP extended request.1.  Conventions Used in this Document   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [ReqsKeywords].2.  The Start TLS Request   This section describes the Start TLS extended request and extended   response themselves: how to form the request, the form of the   response, and enumerates the various result codes the client MUST be   prepared to handle.   The section following this one then describes how to sequence an   overall Start TLS Operation.Hodges, et al.              Standards Track                     [Page 1]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 20002.1.  Requesting TLS Establishment   A client may perform a Start TLS operation by transmitting an LDAP   PDU containing an ExtendedRequest [LDAPv3] specifying the OID for the   Start TLS operation:     1.3.6.1.4.1.1466.20037   An LDAP ExtendedRequest is defined as follows:     ExtendedRequest ::= [APPLICATION 23] SEQUENCE {             requestName             [0] LDAPOID,             requestValue            [1] OCTET STRING OPTIONAL }   A Start TLS extended request is formed by setting the requestName   field to the OID string given above.  The requestValue field is   absent.  The client MUST NOT send any PDUs on this connection   following this request until it receives a Start TLS extended   response.   When a Start TLS extended request is made, the server MUST return an   LDAP PDU containing a Start TLS extended response.  An LDAP   ExtendedResponse is defined as follows:     ExtendedResponse ::= [APPLICATION 24] SEQUENCE {             COMPONENTS OF LDAPResult,             responseName     [10] LDAPOID OPTIONAL,             response         [11] OCTET STRING OPTIONAL }   A Start TLS extended response MUST contain a responseName field which   MUST be set to the same string as that in the responseName field   present in the Start TLS extended request. The response field is   absent. The server MUST set the resultCode field to either success or   one of the other values outlined insection 2.3.2.2.  "Success" Response   If the ExtendedResponse contains a resultCode of success, this   indicates that the server is willing and able to negotiate TLS. Refer   tosection 3, below, for details.2.3.  Response other than "success"   If the ExtendedResponse contains a resultCode other than success,   this indicates that the server is unwilling or unable to negotiate   TLS.Hodges, et al.              Standards Track                     [Page 2]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 2000   If the Start TLS extended request was not successful, the resultCode   will be one of:   operationsError  (operations sequencing incorrect; e.g. TLS already                    established)   protocolError    (TLS not supported or incorrect PDU structure)   referral         (this server doesn't do TLS, try this one)   unavailable      (e.g. some major problem with TLS, or server is                    shutting down)   The server MUST return operationsError if the client violates any of   the Start TLS extended operation sequencing requirements described insection 3, below.   If the server does not support TLS (whether by design or by current   configuration), it MUST set the resultCode to protocolError (see   section 4.1.1 of [LDAPv3]), or to referral. The server MUST include   an actual referral value in the LDAP Result if it returns a   resultCode of referral. The client's current session is unaffected if   the server does not support TLS. The client MAY proceed with any LDAP   operation, or it MAY close the connection.   The server MUST return unavailable if it supports TLS but cannot   establish a TLS connection for some reason, e.g. the certificate   server not responding, it cannot contact its TLS implementation, or   if the server is in process of shutting down. The client MAY retry   the StartTLS operation, or it MAY proceed with any other LDAP   operation, or it MAY close the connection.3.  Sequencing of the Start TLS Operation   This section describes the overall procedures clients and servers   MUST follow for TLS establishment. These procedures take into   consideration various aspects of the overall security of the LDAP   association including discovery of resultant security level and   assertion of the client's authorization identity.   Note that the precise effects, on a client's authorization identity,   of establishing TLS on an LDAP association are described in detail insection 5.Hodges, et al.              Standards Track                     [Page 3]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 20003.1.  Requesting to Start TLS on an LDAP Association   The client MAY send the Start TLS extended request at any time after   establishing an LDAP association, except that in the following cases   the client MUST NOT send a Start TLS extended request:     - if TLS is currently established on the connection, or     - during a multi-stage SASL negotiation, or     - if there are any LDAP operations outstanding on the connection.   The result of violating any of these requirements is a resultCode of   operationsError, as described above insection 2.3.   The client MAY have already performed a Bind operation when it sends   a Start TLS request, or the client might have not yet bound.   If the client did not establish a TLS connection before sending any   other requests, and the server requires the client to establish a TLS   connection before performing a particular request, the server MUST   reject that request with a confidentialityRequired or   strongAuthRequired result. The client MAY send a Start TLS extended   request, or it MAY choose to close the connection.3.2.  Starting TLS   The server will return an extended response with the resultCode of   success if it is willing and able to negotiate TLS.  It will return   other resultCodes, documented above, if it is unable.   In the successful case, the client, which has ceased to transfer LDAP   requests on the connection, MUST either begin a TLS negotiation or   close the connection. The client will send PDUs in the TLS Record   Protocol directly over the underlying transport connection to the   server to initiate TLS negotiation [TLS].3.3.  TLS Version Negotiation   Negotiating the version of TLS or SSL to be used is a part of the TLS   Handshake Protocol, as documented in [TLS]. Please refer to that   document for details.3.4.  Discovery of Resultant Security Level   After a TLS connection is established on an LDAP association, both   parties MUST individually decide whether or not to continue based on   the privacy level achieved. Ascertaining the TLS connection's privacy   level is implementation dependent, and accomplished by communicating   with one's respective local TLS implementation.Hodges, et al.              Standards Track                     [Page 4]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 2000   If the client or server decides that the level of authentication or   privacy is not high enough for it to continue, it SHOULD gracefully   close the TLS connection immediately after the TLS negotiation has   completed (see sections4.1 and5.2, below).   The client MAY attempt to Start TLS again, or MAY send an unbind   request, or send any other LDAP request.3.5.  Assertion of Client's Authorization Identity   The client MAY, upon receipt of a Start TLS extended response   indicating success, assert that a specific authorization identity be   utilized in determining the client's authorization status. The client   accomplishes this via an LDAP Bind request specifying a SASL   mechanism of "EXTERNAL" [SASL]. Seesection 5.1.2, below.3.6.  Server Identity Check   The client MUST check its understanding of the server's hostname   against the server's identity as presented in the server's   Certificate message, in order to prevent man-in-the-middle attacks.   Matching is performed according to these rules:   - The client MUST use the server hostname it used to open the LDAP     connection as the value to compare against the server name as     expressed in the server's certificate.  The client MUST NOT use the     server's canonical DNS name or any other derived form of name.   - If a subjectAltName extension of type dNSName is present in the     certificate, it SHOULD be used as the source of the server's     identity.   - Matching is case-insensitive.   - The "*" wildcard character is allowed.  If present, it applies only     to the left-most name component.   E.g. *.bar.com would match a.bar.com, b.bar.com, etc. but not   bar.com.  If more than one identity of a given type is present in the   certificate (e.g. more than one dNSName name), a match in any one of   the set is considered acceptable.   If the hostname does not match the dNSName-based identity in the   certificate per the above check, user-oriented clients SHOULD either   notify the user (clients MAY give the user the opportunity toHodges, et al.              Standards Track                     [Page 5]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 2000   continue with the connection in any case) or terminate the connection   and indicate that the server's identity is suspect. Automated clients   SHOULD close the connection, returning and/or logging an error   indicating that the server's identity is suspect.   Beyond the server identity checks described in this section, clients   SHOULD be prepared to do further checking to ensure that the server   is authorized to provide the service it is observed to provide. The   client MAY need to make use of local policy information.3.7.  Refresh of Server Capabilities Information   The client MUST refresh any cached server capabilities information   (e.g. from the server's root DSE; see section 3.4 of [LDAPv3]) upon   TLS session establishment. This is necessary to protect against   active-intermediary attacks which may have altered any server   capabilities information retrieved prior to TLS establishment. The   server MAY advertise different capabilities after TLS establishment.4.  Closing a TLS Connection4.1.  Graceful Closure   Either the client or server MAY terminate the TLS connection on an   LDAP association by sending a TLS closure alert. This will leave the   LDAP association intact.   Before closing a TLS connection, the client MUST either wait for any   outstanding LDAP operations to complete, or explicitly abandon them   [LDAPv3].   After the initiator of a close has sent a closure alert, it MUST   discard any TLS messages until it has received an alert from the   other party.  It will cease to send TLS Record Protocol PDUs, and   following the receipt of the alert, MAY send and receive LDAP PDUs.   The other party, if it receives a closure alert, MUST immediately   transmit a TLS closure alert.  It will subsequently cease to send TLS   Record Protocol PDUs, and MAY send and receive LDAP PDUs.4.2.  Abrupt Closure   Either the client or server MAY abruptly close the entire LDAP   association and any TLS connection established on it by dropping the   underlying TCP connection. A server MAY beforehand send the client a   Notice of Disconnection [LDAPv3] in this case.Hodges, et al.              Standards Track                     [Page 6]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 20005.  Effects of TLS on a Client's Authorization Identity   This section describes the effects on a client's authorization   identity brought about by establishing TLS on an LDAP association.   The default effects are described first, and next the facilities for   client assertion of authorization identity are discussed including   error conditions. Lastly, the effects of closing the TLS connection   are described.   Authorization identities and related concepts are defined in   [AuthMeth].5.1.  TLS Connection Establishment Effects5.1.1.  Default Effects   Upon establishment of the TLS connection onto the LDAP association,   any previously established authentication and authorization   identities MUST remain in force, including anonymous state. This   holds even in the case where the server requests client   authentication via TLS -- e.g. requests the client to supply its   certificate during TLS negotiation (see [TLS]).5.1.2.  Client Assertion of Authorization Identity   A client MAY either implicitly request that its LDAP authorization   identity be derived from its authenticated TLS credentials or it MAY   explicitly provide an authorization identity and assert that it be   used in combination with its authenticated TLS credentials. The   former is known as an implicit assertion, and the latter as an   explicit assertion.5.1.2.1.  Implicit Assertion   An implicit authorization identity assertion is accomplished after   TLS establishment by invoking a Bind request of the SASL form using   the "EXTERNAL" mechanism name [SASL,LDAPv3] that SHALL NOT include   the optional credentials octet string (found within the   SaslCredentials sequence in the Bind Request). The server will derive   the client's authorization identity from the authentication identity   supplied in the client's TLS credentials (typically a public key   certificate) according to local policy. The underlying mechanics of   how this is accomplished are implementation specific.Hodges, et al.              Standards Track                     [Page 7]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 20005.1.2.2.  Explicit Assertion   An explicit authorization identity assertion is accomplished after   TLS establishment by invoking a Bind request of the SASL form using   the "EXTERNAL" mechanism name [SASL,LDAPv3] that SHALL include the   credentials octet string. This string MUST be constructed as   documented in section 9 of [AuthMeth].5.1.2.3.  Error Conditions   For either form of assertion, the server MUST verify that the   client's authentication identity as supplied in its TLS credentials   is permitted to be mapped to the asserted authorization identity. The   server MUST reject the Bind operation with an invalidCredentials   resultCode in the Bind response if the client is not so authorized.   Additionally, with either form of assertion, if a TLS session has not   been established between the client and server prior to making the   SASL EXTERNAL Bind request and there is no other external source of   authentication credentials (e.g.  IP-level security [IPSEC]), or if,   during the process of establishing the TLS session, the server did   not request the client's authentication credentials, the SASL   EXTERNAL bind MUST fail with a result code of   inappropriateAuthentication.   After the above Bind operation failures, any client authentication   and authorization state of the LDAP association is lost, so the LDAP   association is in an anonymous state after the failure.  TLS   connection state is unaffected, though a server MAY end the TLS   connection, via a TLS close_notify message, based on the Bind failure   (as it MAY at any time).5.2.  TLS Connection Closure Effects   Closure of the TLS connection MUST cause the LDAP association to move   to an anonymous authentication and authorization state regardless of   the state established over TLS and regardless of the authentication   and authorization state prior to TLS connection establishment.6.  Security Considerations   The goals of using the TLS protocol with LDAP are to ensure   connection confidentiality and integrity, and to optionally provide   for authentication. TLS expressly provides these capabilities, as   described in [TLS].Hodges, et al.              Standards Track                     [Page 8]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 2000   All security gained via use of the Start TLS operation is gained by   the use of TLS itself. The Start TLS operation, on its own, does not   provide any additional security.   The use of TLS does not provide or ensure for confidentiality and/or   non-repudiation of the data housed by an LDAP-based directory server.   Nor does it secure the data from inspection by the server   administrators.  Once established, TLS only provides for and ensures   confidentiality and integrity of the operations and data in transit   over the LDAP association, and only if the implementations on the   client and server support and negotiate it.   The level of security provided though the use of TLS depends directly   on both the quality of the TLS implementation used and the style of   usage of that implementation. Additionally, an active-intermediary   attacker can remove the Start TLS extended operation from the   supportedExtension attribute of the root DSE. Therefore, both parties   SHOULD independently ascertain and consent to the security level   achieved once TLS is established and before beginning use of the TLS   connection. For example, the security level of the TLS connection   might have been negotiated down to plaintext.   Clients SHOULD either warn the user when the security level achieved   does not provide confidentiality and/or integrity protection, or be   configurable to refuse to proceed without an acceptable level of   security.   Client and server implementors SHOULD take measures to ensure proper   protection of credentials and other confidential data where such   measures are not otherwise provided by the TLS implementation.   Server implementors SHOULD allow for server administrators to elect   whether and when connection confidentiality and/or integrity is   required, as well as elect whether and when client authentication via   TLS is required.7.  Acknowledgements   The authors thank Tim Howes, Paul Hoffman, John Kristian, Shirish   Rai, Jonathan Trostle, Harald Alvestrand, and Marcus Leech for their   contributions to this document.Hodges, et al.              Standards Track                     [Page 9]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 20008.  References   [AuthMeth]     Wahl, M., Alvestrand, H., Hodges, J. and R. Morgan,                  "Authentication Methods for LDAP",RFC 2829, May 2000.   [IPSEC]        Kent, S. and R. Atkinson, "Security Architecture for                  the Internet Protocol",RFC 2401, November 1998.   [LDAPv3]       Wahl, M., Kille S. and T. Howes, "Lightweight                  Directory Access Protocol (v3)",RFC 2251, December                  1997.   [ReqsKeywords] Bradner, S., "Key Words for use in RFCs to Indicate                  Requirement Levels",BCP 14,RFC 2119, March 1997.   [SASL]         Myers, J., "Simple Authentication and Security Layer                  (SASL)",RFC 2222, October 1997.   [TLS]          Dierks, T. and C. Allen. "The TLS Protocol Version                  1.0",RFC 2246, January 1999.9.  Authors' Addresses   Jeff Hodges   Oblix, Inc.   18922 Forge Drive   Cupertino, CA 95014   USA   Phone: +1-408-861-6656   EMail: JHodges@oblix.com   RL "Bob" Morgan   Computing and Communications   University of Washington   Seattle, WA   USA   Phone: +1-206-221-3307   EMail: rlmorgan@washington.edu   Mark Wahl   Sun Microsystems, Inc.   8911 Capital of Texas Hwy #4140   Austin TX 78759   USA   EMail: M.Wahl@innosoft.comHodges, et al.              Standards Track                    [Page 10]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 200010.  Intellectual Property Rights Notices   The IETF takes no position regarding the validity or scope of any   intellectual property or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; neither does it represent that it   has made any effort to identify any such rights.  Information on the   IETF's procedures with respect to rights in standards-track and   standards-related documentation can be found inBCP-11.  Copies of   claims of rights made available for publication and any assurances of   licenses to be made available, or the result of an attempt made to   obtain a general license or permission for the use of such   proprietary rights by implementors or users of this specification can   be obtained from the IETF Secretariat.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights which may cover technology that may be required to practice   this standard.  Please address the information to the IETF Executive   Director.Hodges, et al.              Standards Track                    [Page 11]

RFC 2830     LDAPv3: Extension for Transport Layer Security     May 200011.  Full Copyright Statement   Copyright (C) The Internet Society (2000).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Hodges, et al.              Standards Track                    [Page 12]